1. Field of the Invention
The present invention relates to a novel method of manufacturing an exposure mask having an ultramicrostructure for an X-ray exposure method favorable for future use, in rapidly micronizing lithography technique in order to increase the performance of high density integrated circuit and high performance transistors used in the electronics field.
2. Description of the related Art
X-ray exposure lithography technique show promise to break beyond light exposure lithography techniques.
However, X-ray exposure methods are proving to be difficult to implement. As a mask for preventing X-rays, a fine pattern of metal such as gold, tungsten, and the like must be formed having enough thickness to absorb X-rays on a thin film. A widely used technique for drawing a comparatively fine pattern which is not mass-produced at present, is electron beam exposure method which can be combined with the most popular mask manufacturing method namely of forming a fine metal pattern by combining this exposure method with etching, lift-off and plating methods. However, it is very difficult to form an ultrafine metal pattern having sufficient thickness by dispersion in a resist for electron beams to. This is because of the problem of ultramicronization in the electron, beam exposure method or by dispersion in a structure under resist such as metal, substrate and the like, and micronization of about less than 10 nm of frequency is almost limited at present difficult to achieve.
On the other hand, in the formation of a layered structure, it is easy to provide film thickness controllability of about 1 nm. Oblique deposition is one example of a mask using the layered structure, (see Appln. Phys. Lett., 36 (1), 1 Jan. 1980, American Institute of Physics). As shown in FIGS. 1A and 1B, this method forms a mask having a minimum line width of about 2 nm obliquely depositing carbon and tungsten on a periodic square wave polyamide membrane and forms a fine line structure up to 17.5 nm. However, this method reaches a difficult point for minimizing a square wave period because of the use of the oblique deposition method.
At present, the most closely studied method of forming a layered structure is a thin film crystal growing method, compound semiconductor crystal growth, ha been particularly closely studied reaching controllability of switching compositions of less than one atomic layer. At the same time, it is possible to grow crystals on the whole side surface of a deep groove. These advantages are due to crystal growth under such a condition that a growing seed is largely diffused on the crystal surface, thereby maintaining flatness in crystal growth. It is further possible to form a thin film to within one atomic layer unit on the whole crystal growth surface if crystal growth on the thin film is carried out by using an epitaxial growth technique.
X-ray exposure is an exposure method for breaking a limit by wavelength of light exposure with the use of X-rays. However, x-ray exposure introduces the difficulty of manufacturing exposure masks. That is, it is terribly difficult to form a mask which can prevent X-rays on the order of which is 10 nm order required for a very fine X-ray mask.